Method of manufacturing electrical resistances



y 17, 1932- l. SILBERSTEIN 1,859,112

METHOD OF MANUFACTURING ELECTRICAL RESISTANCES .Filed Dec. 11, 1929 Iynyenlbr: .Zs'zcZor flzZZenSfezn nals 10 in the form of caps fixed tothe ends of the carrier and electrically connected with Patented 11.,11, 1932 PATENT OFFICE I SIDOR. SILIBEBSTEIN, 0F iBERLIN, GERMANYmn'r'non or mnuracruzame nrncrmcannnsrsmncns Application filed December11, 1929, Serial No. 413,167, and in Germany December 18, 1928.

-which exact resistances are produced, and

with this object in view my invention consists in first coating theresistance material initially applied to the carrier with a protectivelayer such as lacquer adapted to prevent injury to the resistancematerial by ClllPS or powder cut from the body of resistance materialand the carrier. Other obj ects of the improvements will appear from thefollowing description.

For the purpose of explaining the invention 'a' resistance and anapparatus suitable for manufacturing the same have been shown in theaccompanying drawings, in which Fig. 1 is an elevation partly in sectionshowing a resistance, and

Fig. 2 is a diagrammatical elevation partly in section showing theapparatus for manu-v facturing the resistance.

The resistance illustrated in Fig. 1 comprises a,carrier 1 of insulatingmaterial such as ceramic material, a resistance strip 2 applied to thesaid carrier, a coating 3 of lacquer or other non-conductive material,and termithe resistance material. The strip 2 of resistance material isbounded at both sides by grooves 4 cut into the carrier. In the exampleshown in Fi .1 the resistance stri is in the form of a he ix laid aroundthe cy indrical core 1.

In the manufacture of the resistance I proceed as follows: The carrier 1is first coated with the resistance material 2, which may be for examplea material containing carbon, 1

as is known in the art. The coated core is now exactly measured, andfrom the dimensions thus obtained the breadth and the pitch of thehelical line 4 to be ground into the protective coating, the resistancematerial and the core are exactly calculated so as to obtain the desiredresistance. The blank thus prepared is placed on a lathe, and thetermirials 10 of the carrier 1 are connected with a source ofelectricenergy and an apparatus for measuring current intensities. Preterably Iuse an apparatus such asan ammeter the scale marks of which directlyindicate resistances. Now the-groove 4 is cut into the blank whileobserving the current intensity or resistance indicated by the ammeter,the grinding operation being interrupted when the desired resistance isobtained. Thus by measuring the resistance in the course of the grindingoperation the desired resistance is obtained.

In Fig. 2 I have shown an apparatus in the form of a lathe suitable forcutting the groove 4. In the said figure the blank to be ground hasreceived the reference character 12, which blank is placed on thecenters 5 of the lathe for being rotated thereby. The said centers areengaged by brushes 6 disposed in a circuit including a source ofelectric energy 7 and an ammeter 8 or similar measuring instrument. Thecenters 5 are insulated from the spindles of the lathe by means ofinsulating blocks 11. For grinding the helical groove on the blank arotary grinding disk 9 is provided, which'i's mounted on a Suitableslide-rest 13' by means of which it is adapted to be shifted in thedirection of the arrow :1: while rotating the blank. Thus a helicalroove 4 of the desired pitch is cut through t e protective coating 3,the resistance material 2 nd into the core 1, while the ammeter 8* isobserved, the operation bein interrupted when the ammeter. shows theesired' resistance.

By first coating the resistance material with a protectlve layerI amenabledto produce an exact cut of the resistance strip, the saidresistance strip being held while grinding between the protective layerand the carrier, and any in ury' to the resistance material by chips cutfrom the ceramic material is made impossible.

After cutting the resistance in the man: ner described I coat the blankwith a suitable insulating lacquer by means of which any excess of airor moisture to the resistance material is prevented and the previousinsulation of the resistance material is reestablished.

In my improved method the waste caused by failure in the manufacture isreduced to a minimum, so that the manufacture is economical. g

In the preferred method the carrier 1 of ceramic or other insulatinmaterial is first ground exactly to the desired diameter before applyingthe insulating and protective coatings thereto. By thus producing anexactly cylindrical blank thegrinding operation is made moresatisfactory and more exact. 1

While in describingithe invention reference has been made to aresistance'strip in the form of a helix I wish it to be understood thatmy invention is not limited to the terial to a carrier of insulatingmaterial applying thereto a protective coating, and thereafter removingportions of the said coatings to sired form.

2. The herein described method of manufacturing electrical resistances,which consists in applying a coating of'resistance material to a carrierof insulating material, applying thereto a protective coating, andthereafter cutting from the said layers portions so as to leaveresistances of'the desired form.

3. The herein described method of manufacturing electrical resistances,which consists in applying a coating of resistance material to a carrierof insulating -material, applying thereto a protective coating, andthereafter grinding from the said layers and the surface of the carrierportions so as to leave resistances of the dwired form.

4. The herein described method of manufacturing electrical resistances,which consists in applying a coating of resistance ma thereaftergrinding through the produce the resistance in the deterial to a carrierof insulating material, applying thereto a protective coating, and

layer, the resistance material an into the carrier 'a helical groove ofa shape suitable for leaving a coating of the desired resistance on thecarrier.

Signed at Berlin, this 25th day of November, 1929. I

ISIDOR SILBERSTEIN.

rotective

